One of the most critical times in the life of a magnetic disk file is during the power up of that file. It is at that time that the user may encounter a phenomenon known as stiction, the seizing up of the file. Stiction is evident by the increased force beyond the normal static friction force binding the head and disk surfaces together. Its cause is typically from contamination at the head/disk interface or from excess lubricant.
Numerous strategies are used to combat the effects of stiction. For instance, the disk surface can be textured to decrease the interactive forces between the head and disk. Stiction can be reduced by eliminating materials from the file assembly that have a propensity to outgas organic materials. A third strategY would be the employment of a solid phase lubricant which reduces capillary adhesion and viscous effects.
The prior art illustrates various techniques for overcoming the stiction problem. US patent 4,542,429 shows the application of a radial pulling force applied by the actuator to separate the head from the disk. Japanese patent 58-1858 uses the actuator to apply a minute vibration to the head when the disk rotation starts to release the adhesion between head and disk.
The trend in the disk file business, as in every other element of the electronics industry, is toward miniaturization. As a consequence, the disk file motors are becoming smaller and less powerful. This trend is even more pronounced when the new class of in-hub spindle motors for rotating the magnetic disk assembly is considered. The present invention is directed to spindle motor start technique that overcomes stiction by increasing the effects of existing motor torque and highlights a simple method of implementation and the cost benefits of displacement amplification. The added start torque provided by this method allows a reduction in the cost of spindle motor drive electronics and give better performance than the previous designs. The higher start torque performance represents increased reliability from stiction-type disk file failures.
A previous method for achieving the worst case start torque was to use low on-resistance MOSFETS in a chopper drive scheme. The chopper drive during motor start method uses the motor inductance to produce more DC current in the motor.coil than was taken off the power line. To obtain desired chopper efficiency, the spindle driver needed to have very low on-resistance. This was accomplished by paralleling two power MOSFET bridge drivers.